Current sensing is a critical aspect of today's power management, which is necessary for precision closed-loop control and circuit protection. Traditionally, there are two basic schemes for current sensing, measuring a magnetic field around a current-carrying inductor, or measuring a voltage drop across a sensing resistor. However, a magnetic field measuring circuit is expensive and not that easy to be integrated. And a voltage drop measuring circuit usually employs a precision amplifier to amplify the voltage drop across the sensing resistor which is inserted in a current path. The sensing resistor should have a low resistance, e.g., 1 mohm, for lower power dissipation requirement, so the voltage across the sensing resistor is small, and it is a challenge to provide a precision sensing result while withstanding a common mode voltage having a large range, e.g., the common mode voltage may be as high as 60V, and as low as 0V.